X + 9 = 7 You can throw the X to the right side and change to -X 9 = 7 - X OR You can add both sides with -X X + 9 - X = 7 - X 9 = 7 - X Then you can do the same with 7 by throwing it to the left side and get -7 9 - 7 = - X 2 = - X Now throw the -1 to the left side ( -X = -1X ) 2(-1) = X X = -2